World’s First Fully-Recyclable Electronic Transistor Produced By 3D Printers at Duke University

Duke University engineers have developed the world’s first fully recyclable printed electronics. Its recycling process recovers almost 100% of the materials used and preserves most of its performance capabilities for reuse.

By demonstrating a crucial and relatively complex computing component, the transistor, created with three carbon-based inks, the researchers hope to inspire a new generation of recyclable electronics.

“Silicon-based computer components will probably never go away, and we don’t expect easily recyclable electronics like ours to replace technology and devices that are already widely used,” said Aaron Franklin, Addy Professor of Electrical and Computer Engineering. . at Duke. “But we hope that by creating new, fully recyclable, easy-to-print electronic products and showing what they can do, they can become widely used in future applications.”

Despite the ever-growing pile of discarded electronic devices is now in decline, less than a quarter each year is recycled, according to a United Nations estimate.

Part of the problem is that electronic devices are difficult to recycle. Large plants employ hundreds of workers who hack bulky devices. But while scraps of copper, aluminum and steel can be recycled, the silicon chips at the heart of the devices cannot.

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In the new study, published April 26 in the journal Electronic Nature, Franklin and his lab demonstrate a fully functional, fully recyclable transistor made from three carbon-based inks that can easily be printed on paper or other flexible, environmentally friendly surfaces. Carbon nanotubes and graphene inks are used for semiconductors and conductors, respectively. While these materials are not new to the world of printed electronics, Franklin says, the path to recyclability was opened with the development of a wood-derived insulating dielectric ink called nanocellulose.

“Nanocellulose is biodegradable and has been used in applications such as packaging for years,” Franklin said. “And although people have long known about its potential applications as an insulator in electronics, no one has figured out how to use it in a printable ink before. That’s one of the keys to making these fully recyclable devices functional. “

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The researchers developed a method of suspending nanocellulose crystals that were extracted from wood fibers that, sprinkled with a little table salt, produce an ink that works admirably as an insulator on their printed transistors. Using all three inks in an aerosol jet printer at room temperature, the team shows that its all-carbon transistors perform well enough to be used in a wide variety of applications, even six months after initial printing.

The team then demonstrates how recyclable their design is. By immersing your devices in a series of baths, gently vibrating them with sound waves, and centrifuging the resulting solution, the carbon nanotubes and graphene are sequentially recovered with an average yield of almost 100%. Both materials can then be reused in the same printing process while losing very little of their performance viability. And because nanocellulose is made from wood, it can simply be recycled along with the paper it was printed on.

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Compared to a resistor or capacitor, a transistor is a relatively complex computer component used in devices such as power control or logic circuits and various sensors. Franklin explains that by first demonstrating a fully recyclable multifunctional printed transistor, he hopes to take a first step toward the technology that is commercially pursued for simple devices. For example, Franklin says you could imagine the technology being used in a large building that needs thousands of simple environmental sensors to monitor its energy use or custom biosensor patches to track medical conditions.

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“Recyclable electronics like this are not going to replace an entire half-billion dollar industry in any way, and we are certainly nowhere near printing recyclable computer processors,” Franklin said. “But the demonstration of these kinds of new materials and their functionality is hopefully a stepping stone in the right direction for a new kind of electronics life cycle.”

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